This invention relates to power flow detectors for detecting the direction of power flow.
An electric power supply company must continuously monitor conditions of power demand and supply which can change momentarily. They balance the power demand with the power supply, that is, the delivered power with the generated power. To keep a balance between the power demand and supply, power can be delivered from the systems of other companies. If a balance cannot be held otherwise, power is delivered from other companies which makes up for the power shortage. In such cases, the direction of power flow continuously indicates the condition of power demand and supply. The power company must always monitor those conditions to properly operate the electric power system.
In an electric watthour meter using a time sharing multiplier, the output voltage of the multiplier is integrated and the integrated DC voltage is applied to a voltage-to-frequency converter. The output signal of that converter indicates the power being consumed. In a prior art power flow direction detector, an output voltage of an integrator in the voltage-to-frequency converter is detected. In this case, the power is being delivered if the output voltage of the integrator is positive. If it is negative, the power is being returned from other companies.
Since the integrator is composed of an operational amplifier, the offset voltage of the operational amplifier has an affect on the accuracy of the power flow direction.